6 Car Exhaust Parts Explained (With Labeled Diagram)

By September 2, 2020Performance Modification

An exhaust system is simple – it just pushes exhaust gases out of the vehicle right? Well, not really. Exhaust system is made of many parts and many things happen when exhaust gases pass through it. If you are an enthusiast, understanding all the parts in an exhaust system is a great step towards improving your car game 🙂 Let’s cover each one and also discuss why you would want to replace them with an aftermarket version.

What’s The Function Of An Exhaust System?

Before we begin, let’s first understand what’s the use of an exhaust system. To generate power, a car engine needs to create combustion in the combustion chamber – which in turn generates toxic exhaust gases. A combustion requires oxygen to exist – the more oxygen available, the more powerful the combustion. 

Toxic gases take up space in the combustion chamber – which is why we need to expel them out through the exhaust system. The more we expel the toxic gases, the more room is made available for oxygen to enter – which means more powerful combustion and extra horsepower for the car.

But it doesn’t end there. To protect the environment, we must convert these toxic gases into non-toxic ones before they are expelled out. We must also silence the sound created by the combustion – all these are done in the exhaust system.


With that being said, now we can cover the parts in the exhaust system. I will start with the entrance to the exhaust system all the way till the exit. Look at the labelled diagram below for a quick glance of the exhaust parts.

illustration of a car exhaust system
Exhaust manifold – exhaust gas enters the exhaust system through the manifold
Oxygen sensor – controls how much fuel is injected by reading the amount of oxygen left
Catalytic converter – converts toxic exhaust gases into non-toxic ones
Muffler – silences engine sound
Exhaust pipe – allows exhaust gas to flow in the exhaust system
Exhaust tip – where exhaust gases exit the car

1. Exhaust Manifold

What is the use of an exhaust manifold?

Exhaust manifold is the entrance to the exhaust system. Exhaust gases escape from the combustion chamber through cylinders into the exhaust manifold – where they are combined and flow through the exhaust pipe as one. The number of cylinders depends on your car engine but 4 is typical. Pretty simple right? Exhaust manifold collects the exhaust gases and combines them as one – that’s it.

Why install an aftermarket exhaust manifold?

The stock exhaust manifold works well for the average drivers who are not obsessed with performance. Stock exhaust manifolds are made of cast iron – although cheaper, cast iron is quite thick. Thick manifolds have a narrow diameter, preventing exhaust gases to flow easily. 

Stock exhaust manifolds are also compact with non-uniform lengths. Cylinders in the combustion chamber fire off at different times in a routine. Ideally, only one cylinder in the manifold should deliver gas to the exhaust system at all times.

This is desired so the exhaust gases do not collide into each other at the merging point. The stock manifold having non-uniform lengths do not help with this at all. The delivery and travel time in each cylinder is not consistent. Exhaust gases from different cylinders will definitely collide when they meet in the merging point – unnecessarily increasing backpressure.

Aftermarket exhaust manifold solves all these problems from stock manifold by using stainless steel and uniform lengths. By the way – an aftermarket exhaust manifold is known as an exhaust header. That’s the term I will use now. 

Exhaust header is made of stainless steel – although more expensive, it’s thinner than cast iron. Thinner material means bigger diameter for exhaust gases to flow – increasing the speed of exhaust gases leaving the combustion chamber. This could give you additional horsepower because there’s now more room for oxygen in the combustion chamber. Not to mention stainless steel looks much sexier than a cast iron when you pop open the hood 🙂

Exhaust header also has uniform lengths – although taking more space, the exhaust gases will now flow consistently with equal travel time. The exhaust gases will have lower chance of colliding at the merging point – thus, reducing backpressure. This again – allows exhaust gases to flow out of the combustion chamber quickly. Providing more space for oxygen in the combustion chamber. I cover more about exhaust header and if it improves car sound in this article.

Exhaust Header And Manifold
Aftermarket exhaust manifold (header)
Stock exhaust manifold

2. Oxygen (O2) Sensor

What is the use of an oxygen sensor?

I mentioned to you a car generates combustion to deliver power. In more detail, a combustion is generated when the car engine ignites fuel in the combustion chamber. This combustion absorbs the available oxygen to exist. In summary, combustion requires both fuel and oxygen. Fuel is injected into the combustion chamber while oxygen is sucked from the surrounding. 

The ratio of oxygen and fuel must be optimal. Too much oxygen leftover in the combustion chamber means that performance is not optimal. Not enough fuel is injected to create combustion that utilizes the available oxygen – this means your engine is running lean. Too much fuel injected means that you are wasting your fuel. Not all the fuel can be ignited to create combustion because there’s not enough available oxygen – this means your engine is running rich. Troublesome right? So how can an engine know how much fuel to inject?

Oxygen (O2) sensor comes to the rescue. An O2 sensor is placed in the exhaust system right at the exhaust manifold (more can be placed at different locations). By measuring how much oxygen is leftover in the exhaust gases, your car’s computer can calculate how much fuel should be injected next. Too much oxygen leftover, means more fuel should be injected and vice versa.

illustration of a car exhaust system
Oxygen sensors are commonly found right after the exhaust manifold
Image of Oxygen Sensor
Oxygen sensor. They are plugged into the exhaust pipe.

Aftermarket oxygen sensor?

Aftermarket oxygen sensors exist but they do not provide any benefits like performance or whatsoever. I suggest you only look at aftermarket oxygen sensors only if your existing one breaks and you need a replacement. Different brands of oxygen sensor exist but the difference is only durability. More expensive oxygen sensors are high quality that last longer.

3. Catalytic Converter (CAT)

What is the use of a catalytic converter?

Remember I said a car will convert the toxic exhaust gases into non-toxic ones? Yeah – that’s done by the catalytic converter. Catalytic converter (CAT) contains materials like Platinum, Palladium and Rhodium – which convert the toxic materials into non-toxic ones when exposed to high heat. To be precise, a CAT converts Hydrocarbons, Carbon Monoxides and Nitrogen Oxides into Carbon Dioxide, Oxygen and Nitrogen.

CAT is a very important component in your exhaust system. Without one, your car will emit extremely toxic gases into the environment. Not only is this dangerous to the surrounding, you will definitely fail your emission test. So don’t ever think of removing them!

Catalytic converter
Image of catalytic converter

Why install an aftermarket catalytic converter?

Similar to the oxygen sensor, there’s no such thing as a ‘performance’ catalytic converter. All cars come with catalytic converters in their stock exhaust. You only need to worry about aftermarket catalytic converters if your stock one has malfunctioned and needs replacing. Aftermarket catalytic converters are usually cheaper than OEM ones but have lesser quality. I always recommend you go for the OEM one if you need to replace your catalytic converters.

Not to worry though, a catalytic converter will last for quite a long time. Replacing it is quite rare – unless it is stolen. Stealing CAT is quite common because CAT consists of expensive materials I mentioned earlier (Platinum, Palladium and Rhodium).

Why do people remove their catalytic converters?

To improve performance, car enthusiasts go to extreme lengths and remove their catalytic converters. The idea is that if an exhaust system does not have a CAT, the exhaust gases can flow out much quicker. This is actually true. If you cut open a CAT, you can see that it’s made of small honeycomb structures – which can slow down the flow of exhaust gases. Removing it means the exhaust gases do not have to go through such restriction.

But can a car run without a CAT? Unfortunately, yes it can. A CAT’s sole purpose is to convert toxic exhaust gases into non-toxic ones. Without it, the car can still run properly – it will just emit extremely harmful gases from it’s exhaust. I don’t recommend you do this at all. The performance gain is not so much (below 5 horsepower) and in turn you fail the emission test with flying colors.

Image of straight pipe exhaust
Straight pipe – Exhaust pipe without catalytic converter and muffler

4. Muffler

What is the use of a muffler?

A muffler silences the engine sound from a car. You see – the combustion created in the combustion chamber are explosions with loud noises. To comply with governing laws and to attract the mass market, car manufacturers must keep their car noise down – significantly down. This is where mufflers come to the rescue.

If you cut open a muffler, you will see that it’s made of multiple chambers and metal platings. These platings are designed to cause sound waves to bounce off into the opposite direction – where they collide into other sound waves and cancel each other out. Pretty cool trick, eh? 🙂

Image of the internals of a muffler
Sound waves enter
Sound waves bounced in opposite direction and cancel out each other
Sound waves bounced in opposite direction and cancel out each other

Why install an aftermarket muffler?

I told you that car manufacturers must reduce the car noise down significantly. But what if you actually like those engine sounds and want them louder? This is where an aftermarket muffler comes into place – they contain less platings and do not silence the engine sound as much. This results in a louder and often more aggressive sound. 

Different mufflers produce different sounds. I suggest you listen to the before and after recording first if you ever want to purchase one. I personally enjoy the sound from Flowmaster Super 40. I cover why in this article.

Great sound aside, aftermarket mufflers supposedly can improve car performance. In stock mufflers, the chambers and metal platings could restrict the flow of exhaust gases – causing them to move slowly and get trapped in the exhaust system. This builds up pressure in the exhaust system which makes it hard for more gases to be expelled from the combustion chamber. If you still remember, this means less room for fresh oxygen in the combustion – resulting in weak combustion. 

Aftermarket mufflers with performance in mind are hollow inside. This means exhaust gases flow through quickly and do not build any backpressure. Of course, this also means super loud engine noise because the metal platings that silence the sound waves are not there anymore. I said aftermarket mufflers supposedly improve car performance. What I mean to say is that: In theory, an aftermarket muffler for performance works great. But in reality, not so much. I don’t see aftermarket mufflers providing a significant boost in horsepower. Unless of course you are in a race and need to tune every part of your car for performance.

the internal of performance muffler
Performance muffler are hollow with less platings to allow exhaust gas to flow easily

5. Exhaust Pipe

What is the use of an exhaust pipe?

So far we have seen many components in the exhaust system. Exhaust gases flow through each of them through the exhaust pipe! Exhaust pipes are simply the metal tubing that makes up the exhaust system. Why do I even mention this? Because aftermarket exhaust pipes are quite popular in the performance world. 

Why install an aftermarket exhaust pipe?

The diameter of an exhaust pipe matters a lot – too narrow and the exhaust gases get trapped, too wide and the exhaust gases flow too slowly. Stock exhaust pipes are usually quite narrow – potentially reducing the car performance. Aftermarket exhaust pipes are wider with the right diameter to ensure exhaust gases do not get trapped but can still flow out with speed.

image of flowmaster axleback exhaust
Aftermarket exhaust with bigger piping

6. Exhaust Tip

What is the use of an exhaust tip?

Exhaust tip is the final part in an exhaust system. This is what you usually see from the rear of a car. Stock exhaust tip does not do anything – it’s simply an exit point of your exhaust system. But this doesn’t mean there’s no aftermarket exhaust tip 🙂

Why install an aftermarket exhaust tip?

Aftermarket exhaust tip changes the rear look of your car. Nobody wants an ugly looking tip right?! Also, aftermarket exhaust tips can change the sound of your engine. It works exactly opposite as a muffler. Aftermarket exhaust tips AKA resonator exhaust tips are hollow tubing that are designed to cause sound waves to vibrate in a specific way – to produce louder and more aggressive sound.

A resonator exhaust tip actually works pretty well. Especially when you consider that they only cost about $30 and are easy to install – it’s just a clip on. You will definitely notice your car sounding more aggressive (although not so much louder). Here’s a before and after video for a resonator exhaust tip. You will be surprised 🙂

Image of resonator exhaust tip
Aftermarket exhaust tip that you can clip on your stock exhaust pipe to improve sound


In this short article I have introduced you to all the prominent parts in an exhaust system. Changing an entire exhaust system can provide you much better engine sound and a boost in horsepower. 

If you are looking to purchase one, I recommend you take a look at Flowmaster exhaust. I cover why that is in this article. I hope that helps you in your modding journey 🙂

Ifandi L.

Ifandi L.

Passionate about everything mechanical. Ifandi has been involved with motorcycles and cars since the old days - in his family's auto parts shop. Want to keep in touch? Scream "STRAIGHT PIPEEEEE" at the top of your lungs and Ifandi will show up.

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